The mechanics of patello-femoral joint dysfunction: the usefulness of the Q-angle

Abstract

Patello-femoral joint syndrome (PFJS) is a common problem that is challenging to treat. The dominant theory of its aetiology is „patellar malalignment?, in which the vastus medialis oblique (VMO) muscle is ineffective in controlling patellar position but this is based on assumption. The Q-angle, a frontal plane measure, indicates patellar position relative to the pelvis and tibia; however, there is no standardised measurement protocol and it is assumed to be a fixed value.

The work reported highlights the tension between measurement rigour and clinical utility. Valid measurement of the Q-angle and VMO muscle were established using: motion analysis, magnetic resonance imaging (MRI) and
ultrasound imaging, in recreationally active healthy participants, then applied in various experiments involving people with PFJS, with the following conclusions:

The Q-angle:
* varied over 60 seconds in relaxed standing
* exhibited differences in movement patterns of the three
markers which form the Q-angle between healthy and PFJS
groups during the stance phase of gait
* was generally at its maximum at the beginning of the stance phase of gait and at its minimum at the end
* did not correlate with pronation at the sub-talar joint
VMO muscle size:
* linear and CSA measures of the VMO muscle correlated well
* measures of VMO muscle size from ultrasound were shown to
be valid when compared with MRI and were equally reliable

No correlation between the Q-angle and VMO muscle size was found.

These results increase our understanding of the usefulness of the Q-angle, particularly its natural variation of between 30 and 40 in static standing and its different movement pattern during gait in PFJS. It was established that ultrasound imaging provides valid measures of VMO muscle size and the relationships between its CSA and linear dimensions were characterised.

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Identifiers

ORCID for Maria Stokes: orcid.org/0000-0002-4204-0890

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